This invention relates to an apparatus for delivering a constant airflow across a wide range of restrictions. More particularly, the invention relates to an electronic room air cleaner having a programmable variable speed motor with a built-in constant airflow control for providing a constant airflow in a room and for indicating the presence of a clogged filter.
Smog, dust, pollen, dirt, germs, smoke, and other airborne impurities contaminate the air we breathe. These contaminants can adversely affect our health and comfort, particularly as they are present in our offices and homes. Thus, homes and commercial buildings have employed some form of an electronic room air cleaner to improve the quality of the air we breathe.
Virtually all electronic room air cleaners include a filter to remove dirt, dust, and other unwanted airborne particles from the air within a room. Over time, the filter becomes clogged as the trapped particles accumulate on its surface. This phenomenon is referred to as restriction because, as the filter becomes increasingly clogged, the airflow through the filter is increasingly restricted. When the filter becomes so clogged that the electronic room air cleaner ceases to operate efficiently, it must be cleaned or replaced. But it is difficult to ascertain when a filter needs cleaning or replacement. The rate at which the filter accumulates material depends on many factors such as the season, the activity within the building, the location of the building, the size of the room, and so forth. For example, an air cleaner located in a high-pollen or particularly dusty area will clog more rapidly than it would if located in a low-pollen or low-dust area and therefore require servicing at an earlier time.
A clogged filter restricts airflow in the room. As the airflow in the room decreases, the electronic air cleaner filters less and less air, which causes an undesirable buildup of contaminants in the surrounding air. Current electronic air cleaners are incapable of sustaining a constant airflow over a wide range of different degrees of restriction.
Most electronic air cleaners are capable of detecting a clogged filter by sensing an air pressure differential across the filter. As the filter becomes increasingly dirty, static pressure builds up across the filter. Sensors measure this static pressure, and when the pressure exceeds a predefined limit, the air cleaner unit notifies the operator (usually by means of an alarm or a light emitting diode) that the filter needs servicing. The problem with this clogged-filter detection scheme is that it does not maintain the airflow in the room at a constant rate. The airflow is typically allowed to drop to some extent before the operator is alerted to service the filter. Also, premature servicing of the filter can result, particularly where the unit is operating at high airflow rates. The sensors for detecting a clogged filter are usually calibrated to trigger at the lowest airflow, although some systems include a separate sensor for each different airflow. Multiple sensors increase the complexity and cost of the unit. Single-sensor clogged-filter detection systems make inefficient use of filter media, the most frequently replaced component of such systems.
Therefore a need remains in the industry for an electronic room air cleaner which overcomes the potential disadvantages discussed above while exploiting the advantages of a programmable variable speed motor having a built-in constant airflow algorithm. The present invention as described below addresses this need.